Resistance element



June 14, 1938. K. M. LEDERER RESISTANCE ELEMENT Filed April 20, 1936 Patented June 14,: 1938 PATENT OFFICE RESISTANCE ELEMENT Karl M. Lederer, NewarkfN. J., assigner to Weston Electrical Instrument Corporation,

Newark, N. J., a corporation of New Jersey v Application April 20, 1936, Serial No. 75,441

2 Claims.

' This invention relates to resistance elements and particularly to resistor bulbs for use in the electrical measurement of temperatures.

Systems of this type are employed for many purposes, such as that of maintaining a continuous observation of the temperatures at diiferent points of an airplane engine. Resistor bulbs are inserted in the Water jackets of one or more cylinders, in the lubricating oil system and in the air inlet to the carburetor. Relatively high temperatures are present at the air inlet and some constructions which have been employed for measuring water and oil temperatures have failed yat higher temperatures. Practical considerations as to size, rapidity of response to temperature changes, and ease of replacement present difilcult and conflicting design requirements. The physical structure should be small and rugged, while the resistance "-0 element should be of relatively large size Vor area and in good heat transfer relation to the gas or liquid surrounding the bulb. It has been proposed to obtain a .rapid heat transfer to a Y resistance coil by cementing a prewound coil to i5 the inner wall of a thin metal tube, but this methodloi manufacture is diillcuit and relatively expensive.

Objects of this invention are to provide simple l resistor bulbs which may be conveniently and i economically manufactured. An object is to provide a resistor bulb including a mounting head having a bore therethrough, and an insulating disk located within the head and supporting both the resistance and terminal pins for the same,

if the outer part of the mounting head enclosing the terminal pins and forming a socket for rece iving a, cable plug having terminals complementary to 'the terminal pins. A further object is to provide a resistor bulb having a winding l0 of relatively large diameter wire of high resistance-temperature coefficient, and a compensating windingof wire of low or zero temperatureresistance coefficient for imparting to the resistor bulb the temperaturev characteristics of standard bulbs of copper wire.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

J0 Fig. 1 is a side elevation, with parts broken away, of one embodiment of the invention; Fig. 2 'is an end view of the terminal side of assembled disk and tube;

Fig. 3 is an end view of a resistor bulb having 55 a cable plug inserted in the socket thereof;

Fig. 4 is a fragmentary perspective view of one end of the tube on which the resistance wire is wound;

Fig. 5 is an enlarged fragmentary section of a resistor bulb similar to Fig. 1 but having an 5 added metal protective layer;

Fig. 6 is a fragmentary view of a further modification; and

Fig. 7 is a side elevation of a resistor bulb having a composite winding. l0

In the drawing, the reference numeral i identifies the central section of the mounting head of the resistor bulb, this section being preferably of hexagonal outline to receive a wrench for securing the threaded sleeve section 2 in a tapped l5 hole in an engine cylinder wall or the like. A second sleeve 3 projects from the other end to receive a threaded cap I which secures the cable connections to the mounting head. The cylindrical cable plug 5 of insulating material carries 20 tubular terminals 8 which are provided with screws 1 for clamping the cable leads.

The bore which extends through the mounting head is of somewhat larger diameter at the outer or cable side, and an insulating disk t, preferably of ceramic material, is seated upon the radial shoulder which is thus formed at an intermediate section of the head. The threaded Shanks of the flexible pin contact terminals 9 extend'through the disk ii and are received within au the tubular terminals 5 of the cable plug to provide a wiping contact of low resistance. The contact terminals 8 extend well above the disk 8 and thus decrease the tendency for oil to coilect upon the terminals. Increased Contact re- 35, sistance from oil deposits upon the terminals is a problem which is particularly troublesome with, installations on aircraftbut the long terminals rising above the base of the plug socket and the wiping contacts substantially eliminate errors 49 arising from variable contact resistance atthe cable connections.

A small diameter metal tube I0, preferably of thin copper, is secured to the disk 8 by the bent ends of strap extensions Ii that are formed by cutting away opposite sides of the tube. The lower end 0f the tube i0 is tightly closed by an inserted cap I2 that may be locked in place by a screw i3 by which one end of a copper resistance winding i4 is attached to the tube. The inter- 5g mediate sectionof the tube I0 is coated with a thin layer I5 of a vitreous enamel which is applied by a dipping or spraying operation, followed by baking. The winding il may consist of spaced turns of bare copper wire of small diameter, say 

